The technical portion of an optician's occupation consists in mounting a pair of ophthalmic lenses in a frame selected by a wearer. Such mounting comprises three main operations:                acquiring the shape of the bezel in each of the two rims of the eyeglass frame as selected by the future wearer, in particular acquiring the shape of the grooves running around the insides of the rims of the frame;        centering each lens, i.e. determining the position that each lens is to occupy relative to the frame in order to be suitably centered in front of the pupil of the wearer's eye so that the lens performs properly the optical function for which it is designed; and        shaping each lens, i.e. machining or cutting its outline to the desired shape, taking account of the shape of the bezel and of defined centering parameters, with the machining terminating in a step of making a bezel, i.e. making an engagement ridge on the edge face of the lens so as to hold said lens in the bezel of the frame.        
In the context of the present invention, attention is directed mainly to the third operation of machining the edge face of the lens.
It is well known to perform this operation by means of a shaper device that includes a lens blocking support, a shaper tool that is movable relative to the support, and an electronic and/or computer unit for controlling the position of the machining tool relative to the support. The electronic and/or computer unit is thus adapted to acquire the coordinates of a plurality of points that are felt around the bezel of each rim of the frame, and then to deduce therefrom a control setpoint for the machining tool relative to the support so as to form a profiled engagement ridge on the edge face of the lens.
It is also known to use an optimized feeler and shaper device designed to form a non-uniform engagement ridge on the edge face of the lens so as to take account of variations in the shapes of the bezels of eyeglass frame rims.
Such a device serves in particular to take account of the skew of the bezel, i.e. of variations in the angle of inclination of the bezel around the outline of each rim. This angle of inclination is not negligible in the temple and nose zones of rims, especially when the frame is particularly long or curved.
The device also enables account to be taken of perceptible variations in the shape of the bezel due to each rim of the frame having connections with the bridge, a temple, and a nose pad.
For this purpose, the device is suitable for feeling a plurality of cross-sections of the inside face of each rim and for deducing therefrom, by calculation, an approximation to the three-dimensional shapes of the bezel and of its front and rear margins.
It is then suitable for shaping the ophthalmic lens so that the engagement ridge presents a profile at each axial section of the lens that is not uniform and that is adapted to the shape of the corresponding profile of the bezel of the rim. Thus, once the lens is engaged in the frame, no unsightly gap appears between the rim of the frame and the ophthalmic lens.
Nevertheless, such a feeler device is expensive. It is also particularly time-consuming to use. That device also presents performance that is not always adequate since it does not enable the positions of the nose pads and of the temples of the frame to be determined, and that runs the risk of leaving problems of mechanical interference between the lens and the frame whenever the lens is particularly thick.